1. Field of the Invention
The present invention relates generally to night vision systems of the type which permit vision under very low light conditions by converting incoming infrared and/or visible light from a viewed object to an intensified visible light. More particularly, the present invention relates to a night vision visor system that is compact, light in weight and ejection-safe; and which provides the user with a totally unobstructed peripheral field of view and numerous additional structural and operational advantages.
2. Background Art
Night vision goggles are commonly used by aircraft pilots and others to permit vision under very low light conditions by converting incoming infrared and/or visible light from a viewed object to an intensified visible light.
Prior night vision goggles were typically heavy, cumbersome and unstable. They often resembled television cameras mounted on the user's head, protruding more than 175 mm from the user's eyes, and weighing as much as 850 grams. The weight and front-to-back length of such goggles exerted large moments on the user's head, causing serious instability problems and prevented their safe use in many applications where the user's head was likely to be subjected to high gravitational or centrifugal loads. In emergency situations, for example, when ejecting from an aircraft, there was often not sufficient time to remove the goggles before ejection; and the very substantial forces encountered during the ejection were extremely dangerous to the user.
Night vision goggles are frequently mounted to a helmet adapted to be worn by the user. Helmet-mounted goggles avoid the discomfort sometimes encountered when the goggles are attached directly to the head of the user and provide various other advantages; however, prior helmet-mounted systems also suffer from several inadequacies. For example, in many systems, the structure of the goggles obstructs the user's normal peripheral vision, and thus reduces his peripheral field of view. Many systems also interfere with the proper use of a visor which should generally be positioned in front of the eyes at all times, and other necessary equipment such as an oxygen mask or the like. Many systems are also rather complicated in design, difficult to adjust and generally inconvenient to use.
U.S. Pat. No. 5,254,852 describes a helmet-mounted night vision goggles system that is generally effective in overcoming the above-described inadequacies of the prior art. This patent describes a system in which a compact, light-weight night vision goggles apparatus and a helmet-mounted visor cooperate with one another to ensure that the visor will remain in position in front of the goggles and in front of the user's face to help protect the user, even if the goggles are worn during ejection from an aircraft.
In addition, the night vision goggles apparatus of U.S. Pat. No. 5,254,852 includes first and second housings adapted to substantially cover the left and right eyes, respectively, of the user when the apparatus is in use, and each of the housings contains an optical imaging system for presenting an intensified visible image of a viewed object to a respective eye of the user. The optical imaging systems each include an objective lens system having a light input positioned above the eyes and adjacent a side of the face behind a vertical plane through the eyes so as to not significantly obstruct the normal peripheral vision of the user.
Although, as indicated above, the night vision goggles system of U.S. Pat. No. 5,254,852 is generally effective in overcoming many of the inadequacies of prior art goggles, the system was found not to be fully satisfactory in certain applications.
In particular, the interpupillary distance between a person's eyes is normally about two and one-half inches, and the brain is accustomed to interpreting images received by the two eyes at that spacing. In the system of U.S. Pat. No. 5,254,852, however, the light inputs of the objective optical systems for the two eyes are adjacent opposite sides of the user's head; and, therefore, are more widely spaced than the eyes. This wider spacing between the light inputs for the two eyes results in an effect known as the "hyper-stereo effect" and results in viewed objects appearing somewhat closer than they really are. This effect can become a problem in certain applications such as during landing of an aircraft, for example, on an aircraft carrier or other restricted space.
In addition, night vision systems are typically worn by aircraft pilots who view the surrounding environment through a windscreen which is often quite small and also substantially curved around the edges thereof. Because of the wide spacing between the light inputs of the objective optical systems, the pilot may often have to move his head to one side or the other to avoid looking through the curved portions of the windscreen, which may cause distortion, or to prevent his view from being obstructed by the frame of the windscreen.